Laser-based flow modification to remotely conrol air vehicle flight path

ABSTRACT

Systems, equipment, and methods to deposit energy to modify and control air flow, lift, and drag, in relation to air vehicles, and methods for seeding flow instabilities at the leading edges of control surfaces, primarily through shockwave generation through deposition of laser energy at a distance.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 60/960,976, filed Oct. 23, 2007. The U.S.provisional application, in its entirety, is incorporated herein byreference.

The following patents and patent applications are each incorporatedherein by reference in their entirety:

-   -   1) U.S. Pat. No. 6,527,221, which granted on Mar. 4, 2003,        entitled “Shockwave Modification, Method and Apparatus and        System;”    -   2) U.S. Pat. No. 7,063,288, which granted on Jun. 20, 2006,        entitled “Shockwave Modification, Method and System;”    -   3) U.S. Pat. No. 7,121,511, which granted on Oct. 17, 2006,        entitled “Shockwave Modification, Method and System;”    -   4) U.S. patent application Ser. No. 11/288,425 filed on Nov. 29,        2005 and entitled “Shockwave Modification, Method and System;”    -   5) U.S. patent application Ser. No. 11/540,964 filed on Oct. 2,        2006 and entitled “Shockwave Modification, Method and System;”        and    -   6) International Patent Application No. PCT/US2008/009885 filed        on Aug. 20, 2008 and entitled “Energy-Deposition Systems,        Equipment and Methods for Modifying and Controlling Shock Waves        and Supersonic Flow.”

FIELD OF THE INVENTION

This invention relates to systems, equipment, and methods to depositenergy to remotely modify and control fluid flow along control surfacesof an air vehicle, in order to control its flight path and descent. Theinvention more specifically relates to lasers, acoustic excitation, andablative shock waves, as well as non-lethal vehicle stopping.

BACKGROUND OF THE INVENTION

Air vehicle control is achieved through modifying flow across controlsurfaces, typically by adjusting flaps and angle of attack. Flow alongthe control surfaces can be modified in other ways to allow externalcontrol of the air vehicle. This can be achieved by generatingexcitations to seed instabilities that lead to transitions in the flowalong the control surface, (such as boundary layer separation leading todecreased lift, stall, etc). Several publications discuss this (seebelow for a few), and one general term used to describe the phenomenonis “receptivity” of the specific driving frequency being picked up andamplified as it propagates along the control surface.

Abbott, Ira H.; Von Doenhoff, Albert E.; and Stivers, Louis S., Jr.:Summary of Airfoil Data. NACA Rep. 824 (1945).

Lachowicz, J. M., Yao, C. S., and Wlezien, Richard W.: Flow fieldcharacterization of a jet and vortex actuator, Experiments in Fluids,Volume 27, Issue 1, pp. 12-20 (1999).

Schewe, G., Reynolds-number effects in flow around more-or-less bluffbodies, Journal of Wind Engineering and Industrial Aerodynamics 89,1267-1289 (2001).

Smetana, Frederick O.; Summey, Delbert C.; Smith, Neill S.; and Carden,Ronald K.: Light Aircraft Lift, Drag, and Moment Prediction—A Review andAnalysis. NASA CR-2523 (1975).

Wlezien, Richard W. and Ferraro, P. J.: Aeroacoustic Environment of anAdvanced STOVL Aircraft in Hover, AIAA J. Vol. 30 (11), pp. 2606-2612(1992).

Wlezien, Richard W., Parekh, D. E., and Island, T.: Measurement ofAcoustic Receptivity at Leading Edges and Porous Strips, AppliedMechanics Reviews, Vol. 43, 5, Part 2, pp. S167-S174 (1990).

The basic concept is that certain frequency excitations growexponentially when seeded at the leading edge of a control surface,other frequencies die down and lead to stable flow. Seeding thesefrequencies, even very lightly, can lead to dramatic modification to theflow across the control surface, in particular, in loss of laminar flow,replaced by separated flow, leading to a strong reduction in lift, infact leading to stall under the right conditions (or a dramatic loss inlift). The excitations we will provide are mediated/delivered via laserand much of the pertinent background is described in great detail in theKremeyer patents included by reference. The laser-induced shockwaves weintroduce, either on or near a surface, seed an extremely broadfrequency range, encompassing the unstable (growing) frequencies, aswell as stable (non-growing) frequencies. Even a very weak one-timeintroduction of an unstable frequency is expected to grow, as a result,introduction of the broad spectrum by the shockwaves at the leading edgeis expected to seed all of the growing modes to disrupt flow. Performingthis repeatedly/repetitively will ensure significant and lasting flowdisruption on the targeted control surface.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention relates to systems, equipment, andmethods to deposit energy to modify and control flow along the controlsurfaces of a remote air vehicle.

In another aspect, the systems, equipment, and methods can be used tocontrol the flight path of an uncooperative air vehicle.

In another aspect, the systems, equipment, and methods can be used toground an uncooperative air vehicle.

In another aspect, the systems, equipment, and methods can be based onand deployed from a chase plane.

In another aspect, the systems, equipment, and methods can be based onand deployed from a waterborne craft.

In another aspect, the systems, equipment, and methods can be based onand deployed from a land vehicle.

In another aspect, the systems, equipment, and methods can be based onand deployed from a fixed station.

In another aspect, the systems, equipment, and methods can be comprisedof multiple laser systems, based on any combination of air vehicles,waterborne craft, land vehicles, and fixed stations, targeting anynumber of remote air vehicles.

In some embodiments, the energy deposition can take place in the form ofrepeated shockwaves generated by laser ablation on the leading edge ofcontrol and/or lifting surfaces such as wings, stabilizers, and rotors.

In some embodiments, the energy deposition can be delivered throughrepetition of a focused laser beam.

In some embodiments, the energy deposition can be delivered throughrepetition of a filamenting laser.

In some embodiments, the filamenting laser can deposit the energydirectly onto the leading edge of the control surfaces via ablation.

In some embodiments, the filamenting laser can deposit the energy alongthe leading edge by forming the laser filament parallel to the controlsurface leading edge.

Several embodiments of the invention, including the above aspects of theinvention, are described in further detail as follows, and in theinventions incorporated. Generally, each of these embodiments can beused in various and specific combinations, and with other aspects andembodiments unless otherwise stated herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a pursuit plane employing the laser-basedflow-modification technology to increase drag and reduce lift on oneside of the fleeing air vehicle.

FIG. 2 shows a schematic of a machine-vision view of a target vehicle,allowing the leading edges to be identified and tracked during theensuing target/chase-plane maneuvers.

FIG. 3 shows a shadowgraph image of the expanding shockwave from ananosecond laser energy deposited in atmosphere on an Aluminum surface.

FIG. 4 shows a graph of Lift vs. Reynolds Number for the Growian-Profileat 12 deg AOA. A strong drop in lift results with transitions to/fromlaminar flow (Schewe).

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description, and the accompanying drawings towhich it refers, are provided describing and illustrating certainexamples or specific embodiments of the invention only and not for thepurpose of exhaustively describing all possible embodiments and examplesof the invention. Thus, this detailed description does not in any waylimit the scope of the inventions claimed in this patent application orin any patent(s) issuing from this or any related application.

To facilitate the understanding of the subject matter disclosed herein,a number of terms, abbreviations or other shorthand as used herein aredefined below. These definitions are intended to complement the usagecommon to those skilled in the art. Any term, abbreviation or shorthandnot defined is understood to have the ordinary meaning used by a skilledartisan contemporaneous with the submission of this application.

The term “air vehicle” is used herein to mean any manned or unmanned airvehicle or platform, such as any airplane, launch or re-entry vehicle,space-plane, missile, cruise missile, or the like.

A laser-based approach is proposed modify this flow from a remoteplatform, such as a chase plane (FIG. 1). This approach will allowpreferential modification of control forces to allow external control.This external control will allow steering forces and modified lift to beimposed, in order to steer and/or gradually and safely bring thetargeted aircraft down. More dramatic control can be exerted if calledfor by initiating stall on the wings. This form of external control onthe vehicle is safer and more compelling than the current options ofelectrically/mechanically disabling the vehicle or engaging in riskymaneuvers that can endanger both the target and chase planes/occupants.Any damage to the target vehicle surface will be minimal. There is amarket for this capability in government sectors, allowing smugglers andthreats to be apprehended and/or deterred without risking loss of life.The proposed technology consists of rastering a pulsed laser at rangealong the leading edge of a control surface to preferentially increaseor decrease the “lift” it generates. The drag on the control surface canalso be preferentially increased. The final system will employ machinevision (FIG. 2) to track the control surface leading edges, ensuringsustained application of the externally-applied control throughout thecourse of the chase- and target-vehicle dynamics/maneuvers. The rotorsof rotary aircraft can similarly be disrupted, in fact in certainembodiments, quite simply, by pulse-illuminating the entire rotor (inthe case of a small stabilizing rotor), or a portion of a larger rotor,for example the large lifting rotor. This illumination can modify theflow along the rotary lifting and control surfaces in order to controlboth lift and rotary stabilization.

Vision: Current vehicle stopping technologies, includingelectromagnetic- and mechanical-incapacitation of a vehicle would provevery difficult to employ as a non-lethal weapon against airplanes in aninterdiction scenario. In contrast, the proposed concept is applicablefor use in interdiction missions and is envisioned to be employable andeffective in chase-type scenarios where the targeted aircraft is fleeingfrom the chase plane. The cost of each use will come only from theelectricity required to run the system (with the associated crew, fuel,and plane maintenance). The technology is further anticipated to operateat useful ranges, in excess of 500 m. The proposed technologydevelopment effort stands to yield a system to remotely control afleeing vehicle by adjusting the lift and drag experienced by keycontrol surfaces (control surfaces include both fixed and movingsurfaces, generating lift, drag, and any other forces to enable flightand/or control). This will allow aircraft to be redirected, gentlybrought to a landing, or more quickly removed from the sky by suddenlyinitiating stall on the wings. Rotorcraft have similar considerations,dealing mainly with the upward and stabilizing tail force. Theapplication of external force will be disruptive and confusing to thefleeing pilot, and control can be returned to the fleeing vehicle bysimply disengaging the technology. In any number of chase scenarios,depending on the fleeing pilot's cooperativeness, full control can bereturned to the pilot, moderate external control can be maintained, orthe aircraft can be stalled if necessary. The approach does notnecessarily have to be employed from above and/or behind the targetedvehicle. It can also be employed from below, from the side, or from infront of the fleeing vehicle, or from any position allowing aline-of-sight to the control/lifting surfaces to be affected. Thetechnology also does not need to be housed on a manned chase-aircraft.It can be housed on an unmanned aircraft, a lighter-than-air platform,or a craft in space, or any other craft capable of housing it. Thetechnology can further be housed on stationary structures or surfacecraft, such as land vehicles or waterborne craft, such as unmannedsurface craft, unmanned underwater craft, boats, ships, or submarines.Similarly, a man-portable system can be envisioned.

Technical Rationale: The modification of aerodynamic flows throughcontrolled disturbances has been studied in various forms for manyyears. The localized addition of thermal or acoustic energy can have alarge effect on developing flowfields (e.g. as they propagate along thecontrol surface after flowing across the leading edge). Even if onlyvery small perturbations are seeded at the leading edge, if performedperiodically, within the relatively broad band of unstable drivingfrequencies, these very small seed oscillations will grow as the flowpropagates along the control surface to generate large-scaleoscillations that determine the transition to turbulence and detachedflow. This can strongly affect the performance of the control surface(FIG. 4). These studies have been pioneered by Tollmien, Schlichting,and Goertler. Our application calls for use of a pulsed laser to locallygenerate heating and expansion of the air at the surface of the airfoil's leading edge, thereby providing a flow control perturbationcapable of gross modification of airplane aerodynamics. Known flowmodification schemes, which can be employed, include:

-   -   1) Active forcing of flow transition to turbulence near the        leading edge of an airfoil to increase drag forces;    -   2) Active induction of crossflow vortices near an airfoil        leading edge to increase drag;    -   3) Active flow separation control to locally alter airfoil lift;        and    -   4) Active induction of airfoil separation to stall an airfoil on        demand.

A primary benefit of the proposed laser-induced plasma approach is thatit involves only directed energy and eliminates the need for anythingbut electrical power (e.g. no rounds, propellant, or othermechanical/chemical elements). Furthermore, propagation of the laserenergy through the air is effectively instantaneous and relativelyunaffected by the air/flow. This allows much greaterprecision/reliability in laser -targeting, than when using projectilesor other mechanical/chemical approaches. The adaptive optics methodsrequired to operate over ranges, much greater than those proposed, areavailable, and strong shock generation/expansion and fluid flow due tolaser ablation can be easily demonstrated over long ranges using pulsedlasers. Even weak laser ablation is capable of driving the required seedoscillations. In addition to delivering the ablating energy via focusedor collimated laser pulses, with or without adaptive optics,self-focusing pulses can also be used to generate the ablation for theseed oscillations. The laser filaments that can result from theseself-focusing lasers can yield ablating intensities over very longranges. They can also provide weak seeding over the full length of acontrol surface's leading edge, such as that of a wing, by having thefilament run roughly parallel to the leading edge and very near-by.

One potential defeat mechanism of longer (lower intensity) laser pulsesis for the target aircraft to fly through clouds. This requires thepresence of clouds and will impose its own limitations on the fleeingvehicle's capabilities. In addition to their ability to cause ablationat great ranges, the more exotic, self-focusing (filamenting,ultrashort) laser pulses can be investigated to penetrate fog/clouds, ifthese are of major concern in the mission space of interest. Anunwarranted concern that may be raised is that of damage to the targetsurface. The small damage spots that will result at the target surfaceare anticipated to be no more than a few microns in depth, which fallswell within the roughness tolerances listed in typical maintenancestandards. Their effect will be small, if even noticeable, and thedamage will be mitigated by the desorption of surface water at the pointof laser ablation. Eye safety is also not a significant worry, since aneye-safe wavelength can be employed, and because the laser will targetinert surfaces behind the cockpit (and will not target viewing ports).Eye-safe wavelengths are typically considered to be 1.5 to 1.55 micronsand longer. When the laser pulse encounters the control surface andcreates a plasma, a harmless flash of incoherent visible light will begenerated at the point of illumination (FIG. 7). Finally, concerns maybe raised regarding the ability of the laser to keep up with the leadingedges of interest, as both the chase and target aircraft maneuver. Thehardware and algorithms for this already exist, and since the time oflaser propagation is effectively instantaneous, tracking is notanticipated to be problematic in the final application. Placing areflective coating on the leading edge is not a viable mechanism ofdefeat, since the damage threshold can be exceeded of even the mostreflective surfaces that can be practically incorporated onto a leadingedge. Even if ideal coatings could be employed (which is riddled withpractical impediments), the condensation of water vapor taking place atthe leading edge will serve as the necessary ablatant for the laserpulses to fuel the seed disturbances.

EXAMPLES

The following examples are given as particular embodiments of theinvention and to demonstrate the advantages thereof. It is understoodthat the examples are given by way of illustration and are not intendedto limit the specification or the claims that follow in any manner.

As is illustrated in FIG. 1, a chase plane (102) targets an air vehicle(104) with laser pulses (106 a-e), rastered across the leading edge of acontrol surface.

As is illustrated in FIG. 2, the leading edge of any control surfaces(202), including lifting and stabilizing surfaces can be targeted withrastered laser ablation spots.

As is illustrated in FIG. 3, the laser ablation spots form when asurface (on left edge of each sub-figure shown at different times in theablation evolution.). In this case, the energy deposition is on theorder of hundreds of milliJoules, and the field of view is ˜1.5″,demonstrating a shockwave that expands over inches in tens ofmicroseconds. As the shockwave passes over a given region, it excites avery broad range of frequencies (from a few Hz to tens of kHz) over alarge area. This allows the maximum necessary repetition rate to becalculated roughly, based on simply the size over which the shockpasses. For the case of several inches of influence for each energydeposition spot and many feet of leading edge, the laser will need todeposit tens of laser spots to cover the leading edge once, and it willneed to refresh this line of energy deposition to keep the instabilityseeded and continually excited. If it requires some time for theinstability to die down, we can estimate roughly one excitation forevery few inches to every foot traveled by the targeted air vehicle,resulting in the leading edge having to be rastered across the fulllength at a rate of hundreds of Hz. This yields the need for laser pulserepetition rates of thousands of Hz. Depending on the energy requiredper pulse, the necessary average power of the laser can range from tensto hundreds of Watts. For the alternate geometry, in which the extendedlinear (cylindrical) shock wave of a laser filament is directed nearbyand roughly parallel to the targeted leading edge, similar powerrequirements can be estimated. Assuming a refresh requirement along theleading edge for every cm of travel, we can approximate a laserrepetition rate of tens of kHz, with several mJ of energy required tosustain the filament during each shot, this yields an average power of10's to 100's of Watts.

As is illustrated in FIG. 4, one of the effects that can be sought inthe described control is a significant drop in lift associated with flowseparation that can be controlled through seeding of the correctinstabilities (which are included in the very broad range of frequenciesrepresented in the shockwave generated by either laser ablation at apoint or by a filament in the air). Asymmetrically imposing the dramaticdrop in lift shown in FIG. 4 will provide the ability to turn thetargeted air vehicle and/or eliminate its yaw stability, among otherpossible control schemes. Targeting the tail rotor of a helicopter willalso cause the targeted air vehicle to rotate. Symmetrically targetingthe wings of a fixed wing aircraft will cause the targeted air vehicleto quickly ground itself, while targeting the main rotor of a rotorcraft will also cause it to lose lift. All of the power estimates madefor the instances of targeting large, possibly manned, aircraft arestrongly reduced when considering targeting some of the smaller andslower unmanned aircraft. In these cases, the wing-span can be less by afactor of 5 to 100, and the speeds can be slower by a factor of 2 to100. This immediately reduces the operationally required average powerestimate for a system to counter/control unmanned air vehicles by afactor of 10 and possibly much more, based on how small and slow thetargeted unmanned vehicles are. This places the various ranges ofaverage power requirements at 1-10 kW if wanting to ensure a fullypowered system, 100-1000 W for a system sufficient for most needs, andthen laser systems of 1-1000 W average power for targeting smalleraircraft such as small unmanned air vehicles.

1. An energy deposition system to remotely control one or more airvehicles, comprising: one or more pulsed laser sources to provide theenergy to be deposited; and targeting and control hardware andalgorithms to ensure the correct placement and timing of the laserpulses for the desired control.
 2. The system of claim 1, wherein thecontrol is some combination of active forcing of flow transition toturbulence near the leading edge of an airfoil to increase drag forces,and/or active induction of crossflow vortices near an airfoil leadingedge to increase drag, and/or active flow separation control to locallyalter airfoil lift, and/or active induction of airfoil separation tostall an airfoil on demand.
 3. The system of claim 2, wherein the totalaverage power of the laser system(s) is between 1 and 100 Watts.
 4. Thesystem of claim 2, wherein the total average power of the lasersystem(s) is between 100 and 10000 Watts.
 5. The system of claim 2,wherein the system is located on a chase plane.
 6. The system of claim2, wherein the system is located on one or more waterborne craft.
 7. Thesystem of claim 2, wherein the system is located on some combination ofone or more air vehicles, land vehicles, waterborne craft, and fixedstations.
 8. A method to alter or interfere with the movement of atleast one air vehicle, comprising: depositing energy on, near orproximate at least one control surface of at least one remote airvehicle to modify or control flow along said control surface.
 9. Themethod of claim 8, further comprising: forcing at least one flowtransition to turbulence near a leading edge of said at least onecontrol surface to increase drag.
 10. The method of claim 8, furthercomprising: inducing at least one crossflow vortex near a leading edgeof said at least one control surface to increase drag.
 11. The method ofclaim 8, further comprising: separating of flow control from said atleast one control surface to alter lift of said at least on controlsurface.
 12. The method of claim 8, further comprising: separating offlow control from said at least one control surface to stall said atleast on control surface.
 13. The method of claim 8, further comprising:controlling placement and timing of said deposited energy based oninformation relating to said at least one control surface.
 14. Themethod of claim 13, wherein said information comprises movement of saidat least one control surface.
 15. The method of claim 8, furthercomprising: targeting of said control surface using an electronicprocessor to control placement and timing of said deposited energy. 16.The method of claim 8, wherein said control surface is an airfoil, wing,stabilizer, or rotor.
 17. The method of claim 8, wherein said depositedenergy is in the form of repeated shockwaves.
 18. The method of claim17, wherein said shockwaves are generated by laser ablation.
 19. Themethod of claim 8, wherein said depositing energy comprises: pulsing alaser beam.
 20. The method of claim 8, wherein said depositing energycomprises: pulsing a filamenting laser.
 21. The method of claim 8,wherein said deposited energy is applied directly on a leading edge ofsaid at least one control surface.
 22. The method of claim 8, whereinsaid deposited energy is applied along a leading edge of said at leastone control surface.
 23. The method of claim 8, wherein said depositedenergy is applied parallel to a leading edge of said at least onecontrol surface by positioning the laser filament parallel to at least aportion of said at least one control surface.
 24. The method of claim 8,wherein said altering or interfering comprises remote control.
 25. Themethod of claim 8, wherein said movement comprises flight.
 26. Themethod of claim 8, wherein: said movement is above ground; said movementis in the atmosphere; said movement is in the stratosphere; and/or saidmovement is in space.
 27. A method to modify the aerodynamic flow acrossa surface through the external application of energy.
 28. The method ofclaim 27, wherein the externally applied energy is in the form of asuccession of laser pulses.
 29. The method of claim 28, wherein thesurface is a control surface on an air vehicle.
 30. The method of claim28, wherein the achieved modification results in external control of theair vehicle.
 31. The method of claim 30, wherein the succession of laserpulses is applied to one or more targeted positions along the leadingedge of the control surface.
 32. The method of claim 31, wherein thesuccession of pulses arrive at intervals at their targeted position(s),such that the externally applied energy excites one or more unstablemodes, which grow in magnitude as they propagate along the controlsurface.
 33. The method of claim 32, wherein the laser pulses arefilamenting laser pulses.
 34. A system of controlling an air vehicle, inwhich the leading edge of one or more control surfaces is tracked, inorder to deliver energy to said leading edge, capable of modifying theair flow along said surface(s).
 35. The system of claim 34, wherein theenergy is in the form of successive laser pulses.